diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index b46b6f2..8a30cbe 100644
--- a/.gitea/workflows/build_and_run.yml
+++ b/.gitea/workflows/build_and_run.yml
@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2]
+        day_number: [1, 2, 3]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day3/Cargo.toml b/day3/Cargo.toml
new file mode 100644
index 0000000..0275d9d
--- /dev/null
+++ b/day3/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+regex = "1.11.1"
diff --git a/day3/src/main.rs b/day3/src/main.rs
new file mode 100644
index 0000000..b5b70cd
--- /dev/null
+++ b/day3/src/main.rs
@@ -0,0 +1,57 @@
+use regex::Regex;
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<&str> {
+    Regex::new(r"do\(\)|don't\(\)|mul\([0-9]{1,3},[0-9]{1,3}\)")
+        .unwrap()
+        .find_iter(input)
+        .map(|m| m.as_str())
+        .collect()
+}
+
+fn get_mul_result(mul_instruction: &str) -> u32 {
+    let str_tuple = &mul_instruction[4..mul_instruction.len() - 1]
+        .split_once(",")
+        .unwrap();
+    str_tuple.0.parse::<u32>().unwrap() * str_tuple.1.parse::<u32>().unwrap()
+}
+
+fn part_1(instructions: &Vec<&str>) -> u32 {
+    instructions
+        .iter()
+        .filter_map(|s| match s.chars().nth(0) {
+            Some('m') => Some(get_mul_result(s)),
+            _ => None,
+        })
+        .sum()
+}
+
+fn part_2(instructions: &Vec<&str>) -> u32 {
+    let mut enabled = true;
+    let mut sum = 0;
+    for instruction in instructions {
+        if *instruction == "do()" {
+            enabled = true;
+        } else if *instruction == "don't()" {
+            enabled = false;
+        } else if enabled {
+            sum += get_mul_result(instruction);
+        }
+    }
+    sum
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let instructions = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&instructions));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&instructions));
+    }
+}